<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>

<script>
    class Student {

        constructor(name) {
            this.name= name;
        }

        hello() {
            alert("hello");
        }
    }

    class XiaoStudent extends Student {
        constructor(name, grade) {
            super(name);
            this.grade = grade;
        }
        myGrade() {
            alert("我是一个小神仙");
        }
    }

    let xiaoming = new Student("xiaoming");
    let xiaohong = new XiaoStudent("xiaoHong", 1);

</script>

</body>
</html>